A printed wiring board is an assembly that includes conductive pathways, or nets, etched from copper sheets that are laminated onto a non-conductive substrate. After the nets are formed, electronic components are assembled onto the printed wiring board such that the board mechanically supports and the nets electrically connect the electronic components.
As the speed of electronic circuits and systems on printed wiring boards increases well into the multi-GHz range, properties of printed wiring board nets become an ever more important consideration in the design, development, and manufacture of printed wiring boards. A combination of automated optical inspection, DC continuity, capacitance testing, and DC isolation testing of nets within an image area may be relied upon to screen for potential problems. In addition, printed wiring boards may be tested by measuring for RF impedance defects with manual measurements on coupons fabricated along side the image area. Impedance measurements may also be performed on nets in the image area with a flying head probe tester. However, impedance is only one characteristic relevant to the signal integrity of a link utilizing a printed wiring board transmission line. That is, impedance alone does not fully characterize high speed interconnect, and thus may be inadequate in assessing acceptable interconnect performance. Consequently, when testing misses defects in the transmission line, electronic components may be assembled onto a faulty printed wiring board. Assembling expensive electronic components onto a printed wiring board, and subsequently discovering problems associated with the printed wiring board during system level testing, is a prohibitively costly.